Medical nebulizers that nebulize a fluid into an aerosol for inhalation by a patient are well-known devices commonly used for the treatment of certain conditions and diseases. Nebulizers have applications for conscious, spontaneously-breathing patients and for controlled, ventilated patients.
In some nebulizers, a gas and a fluid are mixed together and directed against a baffle or diverter. In some other nebulizers, interaction of the gas and fluid is enhanced through impacting the gas and fluid against a diverter. The term diverter, as used in this specification, includes any baffle or impinger. As a result of either nebulization process described above, the fluid is transformed into an aerosol, that is, the fluid is caused to form small particles that are suspended in the air and that have a particle size in a range suitable for delivery to a targeted area of a patient's respiratory tract. One way to mix the gas and fluid together in a nebulizer is to pass a quickly moving gas over a fluid orifice tip of a tube. The negative pressure created by the flow of pressurized gas is a factor that contributes to drawing fluid out of the fluid orifice into the stream of gas and nebulizing it.
Important considerations in the design of a nebulizer are the timing and dosage regulation of the aerosolized fluid. In some nebulizer designs, a continuous stream of pressurized gas entrains the fluid against the diverter to constantly generate an aerosol until the fluid in a reservoir is depleted. Continuous nebulization may result in a waste of aerosol during a patient's exhalation or during a delay between inhalation and exhalation. The amount of wasted aerosol may be difficult to quantify and some of the aerosol may be lost to condensation on the nebulizer or mouthpiece during periods of non-inhalation. Nebulizers implementing a timed or non-continuous nebulization may adversely affect particle size and density as the nebulization is turned on and off.
Effective and economical nebulizer therapy includes the ability to quickly generate a large amount of aerosol within a predetermined particle size range. An effective nebulizer preferably provides these features synchronously with the inhalation of the patient. In order to actuate a mechanical nebulizer, a patient's inhalation effort must overcome certain variables. Depending on the structural configuration of the nebulizer, these variables may include one or more of the following: the volumetric flow rate of the flowing gas; air leaks in the device; the force exerted by the flowing gas on a moveable diverter; and the friction between moveable parts. The greater the flow rate, air leaks and friction, the greater the inhalation effort required in order to actuate the device. It is desirable that a nebulizer have adequate sensitivity to quickly respond to an inhalation while not adversely restricting the patient's inhalation.